Preamble based selection diversity in a time division multiple access radio system using digital demodulation

A TDMA (time division multiple access) radio receiver for receiving data bursts each having a plurality of symbols divided into a preamble, a sync word and a data field, the receiver comprising:

• a) a plurality of alternatively connectable antenna channels;
• b) digital demodulation means for digitally demodulating the received data burst before recovery of the sync word;
• c) sync word detection means for searching for the sync word in a demodulated bit stream and generating an indication that the sync word has been received in a previous burst;
• d) timing means for measuring forward in time from reception of the sync word of the previous burst to provide an estimate of the beginning of the preamble of a present burst;
• e) selection means for controlling which of the plurality of antenna channels is connected and for making performance measurements, the selection means connecting the plurality of antenna channels in turn and making a performance measurement for each antenna channel and after all the performance measurements are made the selection means connecting to the receiver the antenna channel with the best performance measurement, the first performance measurement being made during a period having a start time related to the estimate of the beginning of the preamble of the present burst;
• storage buffer means connected to an output of the analog-to-digital converter means, the storage buffer means being large enough to delay the digital samples of the received burst long enough to allow antenna selection without corrupting the detection of sync;
• wherein the digital demodulator means comprises:
• analog to digital converter means for making M digital samples of each symbol, each digital sample containing N bits, where M>0, and N>0;
• and
• slicing means for performing threshold detection on a selected digital sample of each symbol thereby producing a demodulated signal consisting of an estimate of the received data burst.

A TDMA (time division multiple access) radio receiver for receiving bursts each having a plurality of symbols divided into a preamble, a sync word and a data field, the receiver comprising:

• a) a plurality of alternatively connectable antenna channels;
• b) digital demodulation means for digitally demodulating the received data burst before recovery of the sync word;
• c) sync word detection means for searching for the sync word in a demodulated bit stream and generating an indication that the sync word has been received in a previous burst;
• d) timing means for measuring forward in time from reception of the sync word of the previous burst to provide an estimate of the beginning of the preamble of a present burst;
• e) selection means for controlling which of the plurality of antenna channels is connected and for making performance measurements, the selection means connecting the plurality of antenna channels in turn and making a performance measurement for each antenna channel and after all the performance measurements are made the selection means connecting to the receiver the antenna channel with the best performance measurement, the first performance measurement being made during a period having a start time related to the estimate of the beginning of the preamble of the present burst;
• wherein the digital demodulator means comprises:
• analog to digital converter means for making M digital samples of each symbol, each digital sample containing N bits, where M>0, and N>0;
• slicing means for performing threshold detection on a selected digital sample of each symbol thereby producing a demodulated signal consisting of an estimate of the received burst;
• timing recovery means for selecting the selected digital sample for each symbol;
• wherein said timing recovery means compiles a histogram value for each of the M samples over many digital samples, and selects a sample corresponding to the maximum histogram value as the selected digital sample.

A TDMA (time division multiple access) radio receiver for receiving data bursts each having a plurality of symbols divided into a preamble, a sync word and a data field, the receiver comprising:

• a) a plurality of alternatively connectable antenna channels;
• b) selection means for controlling which of the plurality of antenna channels is connected and for making performance measurements, the selection means connecting the plurality of antenna channels in turn and making a performance measurement for each antenna channel and after all the performance measurements are made the selection means connecting to the receiver the antenna channel with the best performance measurement, the first performance measurement being made during a period having a start time related to the estimate of the beginning of the preamble of the present burst;
• c) analog to digital converter means for making M digital samples of each symbol, each digital sample containing N bits, where M>0, and N>0;
• d) digital demodulation means for digitally demodulating selected digital samples of the received data burst;
• e) timing recovery means for selecting the selected digital samples which represent received symbols;
• and
• f) storage buffer means connected to an output of the analog-to-digital converter means, the storage buffer means being large enough to delay all the digital samples of the received burst just long enough to allow antenna selection to be completed without corrupting the demodulation of the sync word.

An antenna channel selection method for use in a TDMA radio receiver having first and second alternatively connectable antenna channels for receiving bursts each having a plurality of symbols divided into a preamble, a sync word and a data field, the antenna channel selection method comprising the steps of:

• a) determining when a sync word for a previous burst from a particular transmitter has been received;
• b) measuring forward in time from the reception of the sync word of a previous burst to provide an estimate of the beginning of the preamble of a present burst from the particular transmitter;
• c) connecting the first antenna;
• d) measuring a first performance measurement for the first antenna channel during a first time interval having a start time related to the estimate of the beginning of the preamble of the present burst;
• e) connecting the second antenna channel during a second time interval following said first time interval;
• f) measuring a second performance measurement for the second antenna channel during a third time interval following said second time interval;
• g) comparing the first performance measurement and the second performance measurement to determine which performance measurement is better;
• and
• h) reconnecting the first antenna channel if the first performance measurement is better.